Composition and process for inhibiting corrosion



Patented Apr. 28, 1936 UNITED STATES PATENT OFFICE COMPOSITION AND PROCESS FOR INHIBITING CORROSION No Drawing. Application July 12, 1934, Serial No. 734,804

9 Claims.

' An object or this invention is to provide new and useful compositions for protecting metals of various kinds from corrosion, especially where metals of difierent kinds are in contact with each other. The compositions in question are homogeneous alcoholic solutions containing certain treating agents which will be described. These compositions are suitable for addition to water in contact with metal, to prevent or minimize the corrosion that would otherwise occur.

A particular object of the invention is to provide highly effective means for protecting the cooling systems of automobile engines or other internal combustion engines from corrosion. A further object is to provide an improved antifreeze alcohol containing small additions of ingredients which do not decompose the alcohol, and which, when the alcohol is diluted as it is when it is in service in the engine cooling system, suppress or minimize corrosion. Another object is to prevent or greatly reduce rusting of the iron parts without causing other parts of the system to be attacked.

Sodium nitrate, or its equivalents, potassium nitrite and calcium nitrite, is compatible with ethyl alcohol and other anti-freeze alcohols, and in their aqueous solutions, is an extremely effectual preventive of rusting and one which does not injure the copper of the radiator. Such nitrite ofiers definite advantages over other additions which have been proposed. It is efi'ective in small amounts, has no color of its own (chromates are highly colored), develops no darkening such as is caused by salicylates, tannates, etc. in presence of iron, does not decompose alcohols (these and organic matter generally quickly decompose chromates; also alkalies, especially alkalies and air are oxidizers of alcohols, and tend to develop both color and odor), and, finally, sodium nitrite adds no odor of its own (unlike pyridine, piperidine and similar organic bases, the protecting action of which toward iron is well recognized).

On the other hand, there is one serious objection to sodium nitrite in these alcohol preparations, which is a gradual attack of the solder of the cooling system, resulting in the slow production of marked quantities of a white insoluble compound at the expense of the solder. The nature of this corrosion product is not known exactly, nor the action by which it is produced and it may be variable according to conditions. It appears most readily on solder surfaces in contact with copper. In automobile radiators the effect is objectionable, not only because of the accumulation of insoluble matter in the system, with consequent danger of plugging up the honeycomb sections, but also because of the possibility of weakening, or eventual opening up, of soldered seams. The present invention is directed to the 5 prevention of this attack without losing the protecting eifect of sodium nitrite on other metals, iron in particular.

The protecting action of sodium nitrite toward iron and also its injurious effect on solder have 10 been known. To suppress the latter effect various additions have been proposed, but tests which have been conducted have demonstrated that the previously proposed additions are either quite ineffectual for the purpose of this inven- 15 tion or, in the case of some of them, that they may delay rather than completely suppress the solder attack in question.

As the result of extensive experimentation and prolonged tests, it has been discovered how to 2 suppress in a striking way this nitrite attack of solder and at the same time retain all the protecting effect of nitrite toward iron and its alloys. Briefly, the discovery consisted in the finding that the full advantage of nitrite can be 25 retained and the solder attack eliminated in aqueous alcohol, by incorporating in the alcohol, in addition to the nitrite, an agent which, on dilution with water, will throw out a neutral and persistent, protecting oil film to coat the metal 30 surfaces.

Kerosene as the film-producing agent has proved entirely satisfactory and for economic reasons is preferred. However, many other oil additions have been shown to give satisfactory 35 film protection capable of protecting the solder of engine cooling systems from attack by nitrite.

In general, any relatively light, chemically-inert oil, sufiiciently soluble in alcohol but substantially insoluble in water, seems to have the desired 40 effect. The fact that kerosene has a low viscosity, and yet is practically non-volatile in the intended me, makes it a desirable addition to the more volatile anti-freeze alcohols (ethyl and methyl), where it is desirable to minimize evaporation as 45 well as suppress corrosion. It has been found, however, that effective oil films can be secured by adding one or a variety of oils, such as castor oil, straight hydrocarbon oils of the machine oil type, lard oil, cocoanut oil, sperm oil and even Ocenol (which represents a different class altogether, being a synthetic higher fatty alcohol with oily-wax characteristics). Oleic acid was tried and functioned as far as producing an oil film capable of protecting the solder, but, probably because of the acidic nature of the oil, the rusting of steel was not prevented. These examples are sui'licient to show that no specific oil film is required, but that its inertness is important.

In non-corrosive alcohol compositions embodying this invention it is highly desirable, though not absolutely essential, to include also a mildly alkaline salt. The advantage of such an addition is that it counteracts instability of the nitrite in the presence of any slight acidity of the alcohol or of the waters that may be put into radiators, in addition to which it serves to disperse a portion of the oil constituent which comes out of solution when the treated alcohol is diluted with water in the cooling system, thereby more efi'ectually insuring the carrying of the oil to all parts of the system and the filming over of the surfaces. A good neutral soap performs these functions admirably and, being cheap and available in uniform and satisfactory condition, is preferred for commercial purposes. However, sodium silicate and other alkali salts of weak acids may be used instead of soap.

The following is given as an example of the invention. An anti-corrosion anti-freeze alcohol is prepared by adding to commercial denatured absolute ethyl alcohol sufiicient of a 40% aqueous solution of sodium nitrite to introduce 0.25 gm. of this salt per 100 c, c. of alcohol, kerosene in the proportion of 3 c. 0. per 100 0,. c. of the alcohol, and 0.09 gm. soap per 100 c. c. of the alcohol. This mixture, homogeneous in itself, gives on dilution with water sufllcient oil separation to coat generously all the metal inside the system and leave sufficient over to come to the top of the liquid in the radiator as a visible layer. It may be explained that dry sodium nitrite could be added instead of its aqueous solution, but the -amount given being near the saturation quantity for commercial absolute alcohol, the rate of solution would be slow. It has been demonstrated both in laboratory and in country-wide use that such a mixture gives perfect protection to the iron and solder of engine cooling systems.

If instead of absolute alcohol, alcohol of ordinary strength, such as 188 proof or more dilute, is used, the amount of kerosene which the liquid will dissolve may be less than desired. In that event the kerosene may be supplemented, or replaced, by an oil of greater alcohol solubility, for example, castor oil.

It will be understood that the proportions of the ingredients given in the example are merely illustrative. Saturated or nearly saturated solutions of nitrite in alcohol are desirable. For commercial absolute ethyl alcohol this amount of sodium nitrite is around 0.25 to 0.30 gm. per 100 c. 0. Much less nitrite will given beneficial results, even though complete protection of the steel may not be realized. As small an amount of nitrite as 0.015 gm, per 100 c. c. of alcohol will reduce rusting of iron or steel. As to the kerosene or other oily body, suflicient must be added to the alcohol to give, after the alcohol is diluted in the radiator, enough oil separation to coat the metal. With ethyl alcohol the amount may be between 1% and 10% on the alcohol, 3% to 5% additions being preferred. As kerosene often is not well purified, it is advisable not to make the amount of kerosene too high, since otherwise there may be a slight attack of copper, not serious mechanically, but giving a greenish discoloration. Soap may be added from 0.01 gm. per 100 c. c. of alcohol up to saturation.

The benefits of the invention are not confined to winter use, since in seasons when the danger of freezing is absent, smaller amounts of homogeneous alcoholic solutions such as have been described may be introduced into engine-cooling -systems to prevent corrosion. For summer use,

the composition should contain a sufficient minor amount of water to hold in solution a larger proportion of sodium nitrite than there is in the anti-freeze compositions, in order to secure adequate rust protection without having an undue amount of alcohol in the cooling system during warm weather. There will be sufficient water in the composition for this purpose if alcohol of 95% strength (by volume) is used, and if the nitrite is incorporated in the alcohol in the form of a solution containing about 6 lbs. of sodium nitrite to 6% gals. of water, for addition to about gals. of the alcohol. Castor oil, or other oil of greater alcohol-solubility than kerosene, may be used as the film-former, or kerosene and castor oil or other combinations of oils may be used in summer anti-corrosion compositions. It will be understood that compositions of this invention may be used to suppress corrosion under divers conditions in which different metals are involved. In addition to iron, copper, lead and the like, the compositions have been found to be. remarkably effective for systems containing aluminum.

The alcohol constituting the predominant part of the composition plays an important part in holding the oil in solution, prior to large dilution with water. If the nitrite were not held in solution in the composition as .sold for use, an uncertain amount of it would be introduced into the water systems. Furthermore, alcohol itself is a retarder of corrosion as compared with water, so that an alcoholic anti-corrosion composition containing nitrite gives better protection for a given amount of nitrite than a purely aqueous solution would. Soap and other alkaline salts are also corrosion retarders and aid in that respect, but their special function in this invention is as a protector for the nitrite, also as an, oil-disperser when the oil separation results from dilution of the composition with water.

While ethyl alcohol has been more especially mentioned, the invention is applicable to antifreeze or radiator alcohols generally, such as methyl alcohol, ethyl alcohol, isopropyl alcohol, glycerol, ethylene glycol, butylene glycol and propylene glycol or mixtures thereof.

The sodium nitrite need not necessarily be added as such to the.alcohol, since it may be formed in the alcoholic solution, by adding sodium ethylate and an excess of an alkyl nitrite, such as ethyl or butyl nitrite. V

While the nitrite is inert to alcohol itself, some of the denaturants used in ethyl alcohol may produce a yellowish discoloration of the solution in the presence of nitrite. Such discoloration is not indicative of loss of protective effect or of corrosion, but to avoid a change in color on long standing and to give the mixture and the radia; tor contents a distinctive appearance, a suitable dye, such as fluorescein, may be incorporated in the treated alcohol.

It will be understood that the foregoing de-' scription is illustrative and that the appended claims are intended to cover such modifications as are within the scope of the invention.

I claim: 1 4

1. An anti-corrosion composition for use in the cooling systems of internal combustion engines and the like, comprising a strongly alcoholic solution containing a small amount of a soluble nitrite of a metal belonging to the group consisting of the alkali metals and alkali earth metals, and an inert film-forming oil.

2. An anti-corrosion composition for use in the cooling systems of internal combustion engines and the like comprising a strongly alcoholic solution containing a small amount of sodium nitrite and an inert film-forming oil.

3. An anti-corrosion composition for use in the cooling systems of internal combustion engines and the like comprising a strongly alcoholic solution containing a small amount of sodium nitrite, an inert film-forming oil, and a mildly alkaline salt.

4. An anti-corrosion composition for use in the cooling systems of internal combustion engines and the like comprising a strongly alcoholic solution containing a small amount of sodium nitrite, kerosene, and soap.

5. A liquid anti-corrosion composition for use in the cooling systems of internal combustion engines, comprising a strongly alcoholic solution containing sodium nitrite, and an inert oil which is held in solution in the composition and which has the property, when the composition is diluted with water, of coming out of solution and providing a persistent protecting film capable of inhibiting corrosion of non-ferrous metal which would otherwise be attacked byv the nitrite.

6. A liquid anti-corrosion composition for use in the cooling systems of internal combustion engines, comprising a strongly alcoholic solution containing a soluble nitrite oi a metal belonging to the group consisting of the alkali metals and alkali earth metals, soap, and an inert oil which is held in solution in the composition and which has the property, when the composition is diluted with water, of coming out of solution and providing a persistent protecting film capable of inhibiting corrosion of non-ferrous metal which would otherwise be attacked by the nitrite.

7. A liquid anti-corrosion composition for use in the cooling systems of internal combustion engines, comprising a strongly alcoholic solution containing sodium nitrite and kerosene, the latter providing a persistent protecting film capable of inhibiting corrosion of non-ferrous metal which would otherwise be attacked by the nitrite.

8. A liquid anti-corrosion composition for use in the cooling systems of internal combustion engines, comprising a strongly alcoholic solution containing sodium nitrite, soap, and kerosene oil, the oil being held in solution in the composition but coming out of solution when the composition is diluted with water and being dispersed by the soap in the diluted mixture to facilitate its filming on the metals of the system to provide a protecting oil film capable of inhibiting corrosion of the non-ferrous metals which would otherwise be attacked by the nitrite.

9. A liquid anti-corrosion composition for use in the cooling systems of internal combustion engines, comprising a strongly alcoholic solution containing a soluble nitrite of a metal belonging to the group consisting of the alkali metals and alkali earth metals, kerosene, and oastor oil.

LLOYD M. BURGHART. 

